Watch Cities Spread Across The Planet Over 5,000 Years

A group of researchers combed through 10,000 data entries to create the first mappable record of human population changes, dating back to 3,700 B.C.
The skyline of Tokyo, Japan. With&nbsp;38 million residents, <a href="
The skyline of Tokyo, Japan. With 38 million residents, Tokyo is the largest urban area in the world.

Cities have grown at such a rapid pace in the last few decades, it’s easy to forget that the world has been urbanizing for thousands of years.

New data from researchers at Yale University turns a piecemeal historical record into a comprehensive and accessible dataset of urban population figures since 3,700 B.C. Independently, Metrocosm blogger Max Galka used their data to map the rise of cities, showing a few thousand years of population changes in his three-minute video. 

In Galka's video, you can see how much urbanization has sped up, from cities slowly appearing in earlier years, primarily located in the Middle East, to the dizzying expansion around the world in the last hundred years. The map marks the date of the earliest recorded population figure for each city, and dot size reflects relative population size, according to Galka's Metrocosm post.

The data Galka used comes from “Spatializing 6,000 Years of Global Urbanization from 3700 B.C. to A.D. 2000," published by the journal Scientific Data earlier this month. The study was conducted by Meredith Reba, a research associate at Yale University's School of Forestry & Environmental Studies, along with Karen Seto, a Yale professor, and Femke Reitsma, a senior lecturer at the University of Canterbury in Christchurch, New Zealand.

They combed through two massive tomes of historical population figures, digitizing, combining and geotagging over 10,000 data entries for more than 1,700 cities.

Their data, however, has multiple limitations -- for example, their sources differ on whether suburbs should be considered in cities’ population totals. Some regions aren't well represented in the data, and some cities are missing population figures for long stretches of time. But even with some inconsistencies and gaps, the expansive dataset could be a valuable resource for further study of cities.

Reba told The Huffington Post she found it most fascinating to see the large declines in population resulting from natural disasters and human conflict like the Crusades.

“To better understand urbanization today it is helpful to know what urbanization looked like through history,” she said in a statement. “By understanding how cities have grown and changed over time, throughout history, it might tell us something useful about how they are changing today.”

This graphic shows the date of the first recorded population figures for each city in the data set the Yale University researchers used. Cities with the oldest data are in red. (The earliest population data figure could be later than when the city began, the researchers note.)

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See larger image here.

The impact of rapid urbanization on the planet is a crucial topic. Cities consume more energy and produce more emissions than non-urban areas, heavily contributing to climate change. Urban expansion is having a major impact on the natural world, paving over important wildlife biodiversity areas and farmland, according to Science Magazine. The new data may give researchers a fuller picture of the relationship between human settlements and the physical environment.

More than half the world’s population now lives in urban areas, according to the United Nations, though Seto recently challenged that figure. She told Undark Magazine last month that it includes small towns and suburbs that don’t match the typical image of an urban place.

Reba, Reitsma and Seto write in their paper that the definition of an urban area varies not only between their data sets, but by historical period and country -- a 200-person settlement qualifies as urban in Norway, they note, while in Japan the threshold for an urban area is 50,000 people. But, they write, there is one thing that remains consistent in the definition of cities, that also helps explain their growth:

“Urban areas are often associated with a higher quality of life than non-urban places, manifested through more opportunities and more services.”  

Kate Abbey-Lambertz covers sustainable cities, housing and inequality. Tips? Feedback? Send an email or follow her on Twitter.   



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